“You can always count on your friends to get you high,” sings Alan Sparhawk, his voice cracking open Low’s 10th album like a creaky door. Likewise, you can always count on Low to get you . . . well, just that. A sampling of Facebook friends asked to listen to “Plastic Cup” yielded interesting results: One struggled to decode its genre, another threatened suicide. This is affirmation of the consistency of Low’s sound, which over 20 years has evened into a sunset-slow Midwest-icana. Ever present are those tense harmonies with drummer (and Sparkhawk’s wife) Mimi Parker, who sings lead more here than on any previous outing. Warm pushes of piano lend songs like “So Blue,” “On My Own,” and “Just Make It Stop” a refreshing bump in gait — this may be the work of producer Jeff Tweedy. If Low’s sound is consistent, so too is the band’s knack for refining it. “The Invisible Way” is as spare, heavy, and lovely as anything Low’s ever done, but it feels essential; there’s an extra beauty to the bleakness of these songs. (Out Tuesday)